This invention relates generally to a drill and more specifically to improvements in a drill having indexable cutting inserts. The drill is of the type shown in U.S. Pat. No. 3,963,365.
Previously available drills of the aforementioned type include indexable inserts to increase the useful life of the drill. The drill commonly is equipped with wear strips to guide the drill for axial movement in substantially a straight line and to prevent the steel body from rubbing against and being worn by the wall of the hole being drilled. In U.S. Pat. No. 4,149,821, such wear strips are eliminated by offsetting the inserts at a particular angular relationship to radially balance the drill.
Drills of the type discussed in the aforementioned U.S. Patents often experience a relatively short service life when drilling hard metals, as metal chips become lodged between the outermost periphery of the drill and the inside of the bore, particularly when the drill is rotated about an upright axis. As friction heats the drill to red-hot temperatures, the chip binding problem becomes more acute. The individual drills are expensive, and the incidences of early drill failure significantly increase the average fabricating cost of a workpiece